Is it really that much of a sure thing?

However, just 55% of the 324 businesses Rice University studied using Groupon between August 2009 and March 2011 reported making any money from the deal. An additional 26.6% lost money and 17.9% broke even in the study.

And while almost 80% of the users visiting these businesses were new customers, only about 20% of them returned to pay full price for goods and services.

And just 35.9% of them wound up spending more than the voucher's face value.

Peddycord, the Pilates studio owner, who also does some marketing consulting on the side, says that was the case with a few restaurants she worked with that did a Groupon promotion.

"There are only so many people for whom this works out," she says, noting that many of these restaurants' servers suffered as Groupon users failed to tip on the original amount.

To be sure, restaurants and spas didn't fare as well in the Rice study, compared with fitness studios, personal trainers, concerts and events, or medical providers such as dentists.

"A dentist has a much higher margin," Dholakia says. "They can afford to give away some services and make less money from it."

Groupon does not track the profitability of its promotions for businesses, says Julie Ann Mossler, a company spokeswoman. But the company insists that its promotions work across all types of businesses.

"It just depends on how you structure the deal," Mossler says.

To be sure, even thriving businesses can suffer if they don't get their deal right.

A business boost becomes a business bust

Rose Nadali says Groupon threatened to take down her Los Angeles laser hair removal business, the Laser Genie, despite her preparations and large base of full-freight customers.

"Very soon after Groupon happened, disaster happened," Nadali says.

Her staff struggled to book appointments for more than 3,000 new customers for a $99 hair removal and body-contouring package (a block of 10 sessions regularly costing more than $2,000).

Even with the addition of three bookers to handle calls, the salon's voice mail and email filled up. People couldn't get through quickly to make appointments or come back soon enough for regular treatments, and even some of her regulars began writing angry reviews on Yelp and other review sites.

Nadali says she tried to keep up, buying another laser machine and staying open until 11 o'clock most nights. But she couldn't. And on top of that, she says, many Groupon users were dishonest, getting refunds from Groupon while still trying to book appointments.

"So many were gaming the system," she says.In the end, Nadali says, the promotion that she thought would generate new customers ran up her credit cards and almost crushed her business.

"Out of 3,085 (vouchers), we got five new customers, and I lost a bit over $200,000," Nadali says. Never again, she vows.

How it goes wrong

Marketing experts say many business owners jump into these promotions before doing enough homework and preparation.

Some do not staff up or stock up enough to handle the onslaught of Groupon-wielding customers, leaving both Groupon customers and their existing client base disgruntled. Coffee shop owners run out of pastries; lines snake down the block as annoyed employees struggle to redeem vouchers. Or it takes months for Groupon users to get appointments.

In some cases, the businesses just can't keep track of the vouchers, leading to frustration for both parties.

Alejandra Sinay, a Los Angeles schoolteacher, says she had an employee at a local Quizno's sandwich shop, to which she brought a Groupon voucher, tell her that her half-full punch card had actually been exhausted, pointing to a printout with tally marks.

"Someone had gone crazy" with these marks, she says, and marked someone else's sandwiches next to her name. The cashier, eyeing her suspiciously, said he had to get the manager, leaving her and other customers waiting at the counter.

In the end, Sinay says, the manager didn't come out, and the cashier said he would give it to her "this time." Meanwhile, she's still owed two more sandwiches from the deal. However, she's dragging her feet about going back, because she knows it will be an ordeal to redeem.

"I don't want to ever go there again," Sinay says.

For some, Groupon just becomes a symbol of guilt and hassle.

Sandra Cunningham, a government consultant blogging on Eruptin.com, a site about post-college life, says she has stopped buying Groupons because they became a "burden" that hung over her whenever she wanted to go out. One unused Groupon in particular, for a local Thai place, temporarily "ruined Thai restaurants for me," she says, because she felt she shouldn't eat elsewhere before using her discount.

After the voucher expired, she says she felt a "kind of a relief" knowing that her dining choices wouldn't be dictated by Groupon.

"The world is full of Thai places, unhaunted by the ghosts of Groupons left unused," she wrote. "Two days later, there is a 97% chance I will be getting a coconut curry at the full menu price and it will be really delicious."

Quality, not price

Cunningham's experience shows why daily deal promotions don't work well for many small businesses.

"Getting people to try your product is very important," says Francois Gossieaux, a partner in marketing firm Human 1.0 who blogged about Groupon. "But if you get it to happen while setting expectations around (low prices), it's not the right way to do it."

A better way to attract and keep customers, retail consultant Phibbs says, is to work on their experience, making products that are more interesting and services that are less forgettable.

"If you are having trouble getting people to the stadium, you build a better ball team," he says.